Heat olive oil in a large pot over medium heat. If using bacon or smoked sausage, add it now and cook until browned (3–5 minutes). Remove and set aside, leaving rendered fat.

Add chopped onion, carrots, and celery to the pot. Sauté for 6–8 minutes until softened and the onion is translucent.

Stir in garlic and tomato paste (if using). Cook for 30 seconds until fragrant.

Add rinsed lentils, diced potato, bay leaf, and thyme. Pour in the broth and 1 cup of water. Stir to combine.

Bring to a gentle boil, then reduce heat to low and simmer, covered, for 25–30 minutes until lentils and potatoes are tender. (Tip: cook for 20 minutes, then check — brown/green lentils soften quicker than large lentils.)

Remove bay leaf and thyme sprig. For a creamier texture, mash a cup of the soup against the side of the pot with a spoon or use an immersion blender for 10–15 seconds — don’t overblend; you want some texture.

Return cooked sausage or bacon (if using). Season with salt and plenty of black pepper. Add 1–2 teaspoons of apple cider vinegar; taste and adjust acidity as desired.

Serve hot, garnished with chopped parsley and a spoonful of yogurt if you like.